COMP-Ang1 accelerates regeneration of ischemia-damaged skeletal muscle through dual regulation

Abstract

Angiopoietin-1 (Ang1), one of the major angiogenic factors, is known to modulate vascular stability, endothelial cells differentiation and survival. However, the direct effect of Ang1 on myoblasts differentiation and the regulatory mechanism remain unclear. In this study, I analyzed the regulatory mechanism of COMP-Ang1 on myoblasts differentiation and found N-cadherin as its receptor required for skeletal muscle regeneration. Tie2 expressing macrophages (TEM), infiltrated by COMP-Ang1, were also found in ischemic muscle for myogenesis acceleration. The ischemic stress in hindlimb stimulated the deterioration of muscle quality and induced the infiltration of inflammatory cells. Interestingly, COMP-Ang1 contributed not only to increase of limb salvage but also significantly to generate regenerating muscle. COMP-Ang1 also increased myotube formation in vitro. Especially, COMP-Ang1 enhanced the expression of myogenin, which is one of important myogenic transcription factors. The mechanism of myogenin synthesis by COMP-Ang1 was regulated by p38MAPK and Ca2+ ion. Interestingly, COMP-Ang1 bound to myoblast surface through N-cadherin but not by M-cadherin and Integrin β 1. COMP-Ang1 increased the p38 MAPK activation through directly binding to N-cadherin and augmented the interaction between N-cadherin and p120-catenin. Moreover, myoblasts that had down-regulated N-cadherin expression by siRNA could not develop myotube despite of existence of COMP-Ang1 in vivo. On the other hand, COMP-Ang1 enhanced the infiltration of macrophages into ischemic muscle compared to control group. Especially, COMP-Ang1 increased the infiltration of TEM (F4/80+Tie2+CD31-) which expresses IGF1, a known myogenic factor, compared with inflammatory macrophage (F4/80+Tie2-CD31-, InfM). TEM isolated from ischemic muscle significantly enhanced the myogenesis of cocultured myoblasts more than both non-treated and InfM groups. Therefore, these results suggest that COMP-Ang1 is a myogenic factor, which acts directly through N-cadherin-p120-catenin-p38MAPK-myogenin axis in myoblasts, and indirectly stimulates TEM recruitment into ischemic muscle to augment acceleration of myogenesis process.